1. Field of Invention
The present invention generally relates to a resource allocation method and an apparatus thereof, and more particularly to a resource allocation for a multi-users multiple input multiple output orthogonal frequency division multiplexing (hereinafter, referred as MU-MIMO-OFDM) system, and an apparatus thereof.
2. Description of Prior Art
Although there were many researches of power and bandwidth allocation method in OFDM systems, these researches usually discussed how to assign power to each sub-channel on the constraint of fixed total power. Recently, the multiple input multiple output (hereinafter, referred as MIMO) system is a main technology researched widely. By using the MIMO system, the transmission rate thereof is enhanced. Because the MIMO system divides its power to each of its antennae, the covering range thereof is smaller that of the single input single output (hereinafter, referred as SISO) system.
In the environment of multi-users, a scheduling algorithm is applied to enhance the signal strength of the antenna which has smallest signal strength, so as to achieve soft coverage enhancement without adding any transmit power to the hardware thereof.
MIMO-OFDM system has become a mainstream technology which enhances the capacity of the wireless communication system, such as IEEE 802.16m WiMax, 3GPP LTE, and so on. Differing from the OFDM system, the sub-channel of the MIMO-OFDM system has a plurality of eigenmode links, and the smallest eigenmode link tends to be affected by the path loss and channel fading. Due to the path loss and channel fading, the signal to noise ratio (hereinafter, referred as SNR) or the capacity of the smallest eigenmode link may not meet the requirements, and therefore link outage may occur. Accordingly, the phenomenon makes each sub-channel of the MIMO system not achieve multiplexing.
In the practical use, because users pay different charges for the internet services provider and transmit different sizes of the transmission data, the communication system must provide a flexible transmission rate for each user. However, there are few researches of resource allocation method for the MU-MIMO-OFDM system when taking the coverage issue in consideration.